In order to reduce emissions levels, it is known to provide fuel injectors in which the total area of the openings through which fuel is delivered can be varied, in use. One technique for achieving this is to use two valve needles, one of which is slidable within a bore provided in the other of the needles to control the supply of fuel to some of the outlet openings independently of the supply of fuel to others of the outlet openings.
Such arrangements have the disadvantages that fuel may be able to flow between the inner and outer needles giving rise to substantially continuous delivery of fuel at a low rate. Further in order to control the movement of the inner and outer needles, separate actuators may be required resulting in the injector being of increased complexity.